The present invention relates generally to instruments and techniques for preparing a site between two adjacent bony segments to receive an implant therebetween. More specifically, the present invention provides instruments for vertebral end plate preparation to receive interbody fusion devices or artificial disc implants. The instruments and techniques of the present invention have particular application, but are not limited to, direct anterior or oblique-anterior approaches to the spine.
While implants of various types have been utilized throughout the body for various orthopedic bone applications, the present invention has particular application to the field of preparing an intervertebral disc space to receive an interbody fusion device to create bony fusion or a spacer providing artificial disc functions. Such procedures may be necessary where the natural disc has degenerated or slipped resulting in pain and discomfort to a patient. The deterioration or movement of the disc often results in the two adjacent vertebral bodies coming closer together. A common treatment is to surgically restore the proper disc space height to thereby alleviate the neurologic impact of the collapsed disc space. Typically, the damaged disc is removed and an alternative substance is inserted to maintain the proper height. While artificial discs have been developed and will likely continue to be developed that may be placed in the effected disc space, present procedures often utilize a load bearing structure, either man-made or natural, to maintain the disc height and promote bony fusion between the adjacent vertebrae. Such techniques for achieving interbody fusion between adjacent vertebral bodies is well-known in the art, it will not be described further.
U.S. Pat. No. 5,772,661 to Michelson discloses methods and instrumentation for surgical correction of human thoracic and lumbar spinal disease from an anterior, lateral aspect of the spine. This patent discloses methods, techniques, and instruments for lateral placement of spinal implants. While the application does recognize that an approach from a lateral aspect of the spine in an area of lordosis may result in angulation between the end plates adjacent vertebra, this invention teaches only restoration of the proper angle between the vertebra. Subsequent preparation of the opening to receive an implant, however, is created by over cutting into the end plates of the adjacent vertebra disposed closest and potentially under preparing the end plates disposed farther apart. Thus, there is a need for end plate preparation which not only maintains lordotic angulation of adjacent vertebra, but also provides for substantial uniform preparation of the vertebral end plates to receive an implant.
International publication WO 98/04202 published Feb. 5, 1998 discloses milling instrumentation and methods for preparing a space between adjacent vertebral bodies. This publication discloses utilization of a milling device to control the depth of penetration and field of cut of cutting instruments adapted to prepare vertebral end plates to receive an implant. However, as with earlier approaches to end plate preparation, this publication fails to teach instruments utilized to provide precise control over cutting depth, height, and angulation. Such drawbacks are particularly acute when it is considered that an oblique approach to the anterior spine may be necessary where patient anatomy does not permit easy direct anterior access to the spine.
Thus, there remains a need for improved instrumentation and techniques for disc space preparation. The present application is directed to those needs.